This script can be used to show the top 10 SQL activity for the last hour.
It uses the v$active_session_history view to search top SQL by resource consumption.

Top 10 SQL Activity

SELECT trunc(sample_time,'MI'),
       sql_id,
       count(sql_id) as TOTAL
FROM v$active_session_history
WHERE sample_time between sysdate - interval '1' hour and sysdate
AND sql_id in (select sql_id from (
 select
     SQL_ID ,
     sum(decode(session_state,'WAITING',1,1))  as TOTAL_ACTIVITY
from v$active_session_history
WHERE sample_time between sysdate - interval '1' hour and sysdate
group by sql_id
order by sum(decode(session_state,'WAITING',1,1))   desc)
where rownum < 11)
group by trunc(sample_time,'MI'),sql_id 
order by trunc(sample_time,'MI') desc

Here is the result you can obtain:

and the active sessions history graph for the same period: